In extrusion blow moulding of plastic products, moulding tools comprising two mould-halves which are configured complementary to one another and jointly delimit a mould nest are usually employed. A thermoplastic extrudate, usually in the form of a tube, is placed between the open halves of the tool. The tool is closed around the preform, which is applied inside the tool against the interior wall of the cavity formed by the tool, so that the finished article has an outer form corresponding to the inner contour of the moulding tool. The shaping of the preform inside the cavity of the tool is effected either by expanding the preform by means of gas pressure or by applying the preform against the inner wall of the tool by means of negative pressure, which is exerted via channels in the inner wall of the mould.
If components are to be placed inside a product to be produced in this manner, the part concerned is placed by means of a holder between the open mould parts in such a manner that the tube-shaped extrudate surrounds the component around which blow moulding is to take place. The mould parts are then closed around the tube and the component received therein. Depending on the type of fastening of the component inside the container to be produced, further slides, component holders, dies or the like are required.
In another known method for extrusion blow moulding of hollow bodies, web- or strip-type extrudates are continuously extruded into an open tool from above, or removed from an extruder by means of a manipulator while still in a plastic state, and introduced between the open parts of the tool. Such a method has advantages with regard to introducing built-in parts into the container to be produced.
Such a method is known, for example, from DE 10 2006 031 902 (filed at the German Patent and Trade Mark Office on Jul. 7, 2006). Reference is made here to the contents of this disclosure in their entirety. In the method known from DE 10 2006 031 902 web- or strip-type preforms of plasticised material are shaped in a multi-part tool, which forms a mould nest, through expansion and application of the preforms against the inner contour of the mould nest. Two mutually complementary intermediate products in the form of shells are formed first. Built-in parts are then fastened to the inner faces of the shells, which are oriented towards one another in the installed position. The shells are then joined together and welded to one another by their peripheral, flange-like edges to form the finished hollow body.
The attachment of built-in parts to the inner wall of an intermediate product which has been obtained using a method described above is also known, for example, from US 2008/006625 A1, filed at the USPTO on Mar. 7, 2007, to the contents of which reference is made here in their entirety.
Finally, such a method is known, for example, from DE 10 2006 027 256 A1, filed at the German Patent and Trade Mark Office on Sep. 6, 2006, to the contents of which reference is likewise made here in their entirety. This document relates to a moulding tool for producing extrusion blow moulded products in the above-described form. This moulding tool comprises two outer moulds and a central mould. The outer moulds and the central mould are displaceable away from and towards one another in the sense of an opening and closing movement of the tool. The central mould is provided with component holders as the manipulation device, which component holders can be moved into and out of the tool plane defined by the central mould. The component holders are in turn arranged on a carrier which is also displaceable with respect to the central mould.
All the above-mentioned methods are characterised in particular by the advantage that the introduction of built-in components into the container to be produced is comparatively simple. Other manipulations on the inner wall of the container to be produced are also readily conceivable, and are comparatively simple to implement.
However, in practical application the fastening of built-in parts inside the hollow body has proved difficult. The thermoplastic material for producing the containers usually consists of an extrudate with one or more barrier layers, adhesive agent layers and outer and inner layers of polyethylene. Fastening of components to the wall of the intermediate product is possible either in a form-fitting manner by locking, or by a type of riveting as known, for example, from DE 10 2006 006 469, or by welding. In the case of riveting, which is preferably carried out without additional riveting dies or the like, the warm-plastic material of the intermediate product is pressed through arcuate openings of the built-in part, where the warm-plastic material flows behind the openings in the manner of a rivet head and forms a form-fitting connection upon cooling. This has the advantage that the component does not need to be made of a compatible plastics material in terms of weldability. In the case of welding, by contrast, the plastics materials used for both the built-in component and the intermediate product must be compatible with one another. In either case, with this type of introduction of built-in components, contact between the built-in component and the still warm-plastic or hot-plastic wall of the intermediate product is problematic. Upon a first contact, sudden zonal cooling of the intermediate product takes place, which in the case of production of a welded connection is detrimental to the quality of the welded connection. In addition, through differential cooling of the wall of the intermediate product sunken areas can be produced at different points on the finished product, which are also undesirable.